We are studying the organization and function of the tumor virus polyoma, and are especially interested in the origin of DNA replication, the nature of the RNA splice sites and the identification and characterization of the splicing enzymes, and the mechanisms of cell transformation. We are currently concentrating on the construction of mutants and recombinants to be used as substrates for assays of putative splicing enzymes, and the characterization of the splice sites of the early and late messenger RNAs. A major new interest that we are beginning to pursue is the construction and study of polyoma cloning vehicles.